[3.16.y-ckt stable] Patch "RDS: fix race condition when sending a message on unbound socket" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    RDS: fix race condition when sending a message on unbound socket

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b8ff93b544fec0b515d4cf880ffdf19b60aab3b8 Mon Sep 17 00:00:00 2001
From: Quentin Casasnovas <quentin.casasnovas at oracle.com>
Date: Tue, 24 Nov 2015 17:13:21 -0500
Subject: RDS: fix race condition when sending a message on unbound socket

commit 8c7188b23474cca017b3ef354c4a58456f68303a upstream.

Sasha's found a NULL pointer dereference in the RDS connection code when
sending a message to an apparently unbound socket.  The problem is caused
by the code checking if the socket is bound in rds_sendmsg(), which checks
the rs_bound_addr field without taking a lock on the socket.  This opens a
race where rs_bound_addr is temporarily set but where the transport is not
in rds_bind(), leading to a NULL pointer dereference when trying to
dereference 'trans' in __rds_conn_create().

Vegard wrote a reproducer for this issue, so kindly ask him to share if
you're interested.

I cannot reproduce the NULL pointer dereference using Vegard's reproducer
with this patch, whereas I could without.

Complete earlier incomplete fix to CVE-2015-6937:

  74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")

Cc: David S. Miller <davem at davemloft.net>
Reviewed-by: Vegard Nossum <vegard.nossum at oracle.com>
Reviewed-by: Sasha Levin <sasha.levin at oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar at oracle.com>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas at oracle.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Cc: Moritz Muehlenhoff <jmm at inutil.org>
Cc: Kamal Mostafa <kamal at canonical.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/rds/connection.c | 6 ------
 net/rds/send.c       | 4 +++-
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/net/rds/connection.c b/net/rds/connection.c
index f5fb7d6b7c41..378c3a6acf84 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -183,12 +183,6 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
 		}
 	}

-	if (trans == NULL) {
-		kmem_cache_free(rds_conn_slab, conn);
-		conn = ERR_PTR(-ENODEV);
-		goto out;
-	}
-
 	conn->c_trans = trans;

 	ret = trans->conn_alloc(conn, gfp);
diff --git a/net/rds/send.c b/net/rds/send.c
index 23718160d71e..dfca46865d2e 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -955,11 +955,13 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
 		release_sock(sk);
 	}

-	/* racing with another thread binding seems ok here */
+	lock_sock(sk);
 	if (daddr == 0 || rs->rs_bound_addr == 0) {
+		release_sock(sk);
 		ret = -ENOTCONN; /* XXX not a great errno */
 		goto out;
 	}
+	release_sock(sk);

 	/* size of rm including all sgs */
 	ret = rds_rm_size(msg, payload_len);